1. Field of the Invention
The present invention relates to a movable-member supporting apparatus which is suitable to support a movable member such as an optical pickup. In the movable-member supporting apparatus according to the present invention, a flexible portion which is bent in response to a motion of the movable-member is provided in the vicinity of a fixed end portion.
2. Background
FIG. 1 is a perspective view showing an optical pickup. In the drawing, an objective lens 1 is fixed to a cylindrical member 2 to converge light and irradiate a disk (not shown) with the converged light. The cylindrical member 2 is fixed to a bobbin 3. Focusing and tracking coils 4 and 5, respectively, are attached to an outer circumference of the bobbin 3. Those parts described above constitute a movable member. The movable member is provided with a supporting portion 6 which is supported by a supporting member (or suspension) 7 and connected to a fixed member 8 through the supporting member 7.
When a focusing or a tracking error signal is supplied to the coil 4 or 5, respectively, the coil 4 or 5. which is disposed in a magnetic field of a magnet (not shown), receives an electromagnetic force, so that the movable member moves in the focusing direction (FIG. 2(b)) or in the tracking direction (FIG. 2(a)), respectively. As a result, the focusing/tracking state of light impinging onto the disk through the objective lens 1 is controlled.
FIG. 4 shows the structure of the above-mentioned supporting member 7. In the drawing, a wire 11 is surrounded by a rubber material 12. Being flexible, the wire 11 can make the movable member move in the focusing/tracking direction. The rubber material 12 is provided to suppress unnecessary vibrations of the wire 11.
In the thus constituted supporting member, however, it is difficult to prevent (absorb) resonance of the supporting member in the axial (longitudinal) direction. As shown in FIG. 3. when resonance is generated in the supporting member 7 in the longitudinal direction (the direction A in FIG. 3) thereof, the movable member (which includes the bobbin 3 and the objective lens 1 supported by the bobbin 3) is rotated in the direction B in FIG. 3 within a plane parallel to the sheet of the drawing.
FIG. 5 shows the structure of a supporting member arranged so as to absorb the above-mentioned resonance in the longitudinal direction. The supporting member 7 has end portions 21 fixedly attached to a movable member and a fixed member, respectively, the end portions 21 being connected to each other through a connecting portion 22. The connecting portion 22 is formed of a pair of corrugated portions 23 and 24 formed in a corrugated shape and a pair of linear portions 25 and 26 formed in a substantially linear shape and disposed at a center between the corrugated portions 23 and 24. Each of the corrugated portions 23 and 24 connects the pair of end portions 21 to each other. The linear portions 25 and 26 are connected at their one ends to the respective end portions 21 and extended from the latter, the other ends of the linear portions 25 and 26 overlapping each other at a substantially central portion between the end portions 21. The overlapped portion of the linear portions 25 and 26 are not connected with each other but are separated from each other.
The connecting portion 22 is bent in the direction substantially perpendicular to the sheet plane when the connecting portion 22 moves in the focusing direction, and bent in the direction substantially parallel to the sheet plane when the connecting portion 22 moves in the tracking direction, as viewed in FIG. 5.
On the other hand, for example, if the connecting portion 22 moves by .DELTA.X in its longitudinal direction as shown in FIG. 7, the overlapped portions of the respective linear portions 25 and 26 are elongated (or shortened) correspondingly and the corrugated portions 23 and 24 are elastically transformed. A vibration-suppressing member 27 is attached at a position (a substantially longitudinal center of the connecting portion 22) where the linear portions 25 and 26 are overlapped on each other. As shown in FIG. 6, the vibration-suppressing member 27 is constituted by an absorbing member 31 made of a viscoelastic member (it suffices to apply only a viscoelastic agent), rubber, or the like, and a supporting member 32 made of aluminum foil, or the like, for supporting the absorbing member 31. Since the absorbing member 31 absorbs motion of the linear portions 25 and 26, the resonance in the longitudinal direction is prevented from being generated.
In the conventional movable-member supporting apparatus as shown in FIG. 5, resonance in the longitudinal direction can be prevented from occurring as described above, however, there is less vibration-suppressing effect against the displacement in the essential focusing/tracking direction. Accordingly, there is such a disadvantage that the Q factor (peak quantity) at a low-band resonant frequency becomes large to about 30 dB as shown in FIG. 8.